Crystal oven



c. w. MANN 2 915 653 Dec. 1, 1959 CRYSTAL OVEN Filed Kay 17, 1957 2 Shuts-Sheet 1 INVENTOR. CHARLES W. MANN ATTORNEY.

C. W. MAN N CRYSTAL OVEN 2 Sheets-Sheet 2 INVENTOR. CHARLES W MANN A TpR N EY.

rim Kay 17. 1957 United States Patent CRYSTAL OVEN Application May 17, 1957, Serial No. 659,894 1 Claim. c1. 310-4-9) The invention relates generally to I piezoelectric frequency control apparatus'more particularly to a temperature regulated oven for piezoelectric units for maintaining such crystal frequency control elements at a constant temperature irrespective of variations in the ambient temperature in which the apparatus employing the crystal oven'may be'used j Many'arrangements are known in the prior art for maintaining a piezoelectric crystal withinaset of nested containers having insulating material the'rebetween" with thermostatically controlled heater means for maintaining the crystals at a constant temperature. While these arrangements have provided generally satisfactoryoperation they involve relatively complex construction-and assemblytechriiques and do not provide 'all'of 'the operating features and versatility in manufacture and'adjustm'e'nt which are-desirable in this type of equipment.- a

It "is an objectof this-invention to provide a thermostatically controlled constant'temperature enclosure for a plurality of piezoelectric elements'which is relatively simple to manufactureand to maintain while providing extremely accurate temperature control for the enclosed crystal units." i a -*It is a furthe'r' object of this invention to provide a temperature regulated crystal enclosure which is protected against excessive temperatures resulting from malfunctioning of the thermostat.

' AfurtherQobject of this invention is-to provide a temperature controlled crystal unit inwhich circuit adjustmentsmay be accomplished within the unit to adapt the crystal elements "containedtherein to the particular circuit in whichthey are to be used in order to obviate such adjustments in the'cquipment itself.

An-additional object of this invention is to provide a temperature regulated crystal enclosure which makes provision for laboratory or manufacturers adjustment of the electrical characteristics of the crystal unit at the time of manufacture whereby :the completed unit may be sent to the ultimate user in condition for immediate use in the frequency controlled equipment. v.

An additional-object ofthis invention is to provide a temperature regulated crystal enclosure which may be assembled and disassembled for the purpose of substitutingditferent; piezoelectric crystals or for repair and maintenance purposes without altering in any way the critical lead dress associated with the crystal signal circuits.

These and other objects of;the present invention are achievedby means of an oven which comprises a cylindrical inner housing which contains a thermostatic con- 1 trolelement symmetrically disposed with respect to the mounted position. of two piezoelectric crystals. Within this-housing also are'located a thermal overload contact and a thermal anticipator element which is in direct thermal contact with the thermostatic unit but is insulated from the housing itself and extends to be in direct thermal. contact with the external housing which surrounds the whole unit and is in communication with the ambient temperature. 1 The inner housing issurrounded by heat- 2,915,653 Patented Dec. 1, 19 59 er windings which are connected by means of leads to the appropriate power terminals. The inner cylindrical unit is mounted on an end supporting plate which also supports a terminal board and the sockets for the piezoelectric crystals. The crystal sockets are electrically connected to the terminal board while the terminals on the terminal board are connected to the plug-in socket which is mounted in the supporting base of the unit. In this manner the compact oven assembly is provided with means for adjusting the circuit constants associated with the crystals and at the same time provides accuratev temperature control in a unit which is readily manufactured and easily serviced.

A complete understanding of the present invention will be obtained in the following detailed description taken in conjunction with the accompanying drawings in which:

Fig. l is a perspective view of the crystal control unit in its'disassembled position providing for the replacement of the crystal units;

Fig. 2 is a side elevation view partly in section of the completely assembled crystal oven;

Fig. 3 is an elevational view of the power terminals of the oven; and

Fig. 4 is a schematic wiring diagram showing the connections of the signal and power elements in the temperature control unit.

1 Referring now to Fig. l, a base 11 of Bakelite or other suitable insulating material is provided for supporting the entire assembly. The base 11 has a centrally located hole' in which is mounted an octal socket 12 or other conventional plug connector member. Supported inperpendicular relation to the base 11 is a supporting plate 13 which is secured to the base 11 asymmetrically with respect to the centrally mounted octal plug 12. The plate 13 contains threaded holes for receiving retaining screws 14 along the edge thereof and has a large hole 15 therein and a slot 16 cut in the bottom edge thereof.

On one face of the plate 13 are mounted two crystal sockets 17 which provide two terminal receptacles for receiving the plug'terminals of the crystal units to be enclosed within the temperature control oven. The crystal sockets 17 are secured to the plate 13 by means of screws 18 or other conventional fasteners which also support the terminal board 19 in parallel coextensive relation with plate 13. Terminal board 19 has two rows of solder 'terminals'supported thereon to which are removably connected suitable circuit components such as-resistors 22 and capacitors 23. The electrical connections between the terminals of the crystal sockets 17, solder terminals 21 on the terminal board 19, and the pins of socket 12 are made as herein after described.

The inner enclosure for the crystal units comprises a cylindrical shell 25 preferably of copper which is shaped to fit the edge of plate 13. The shell 25 contains in one edge thereof slotted recesses 26 which slidably engage the screws 14 in the edge of the plate 13 when the unit is assembled for supporting the cylindrical shell 25 on the plate 13. The cylinder 25 supports on the outer surface thereof a pair of heater windings 27 which are in intimate thermal contact with the shell 25 and suitably supported thereon and protected by a coating of thermo-v setting resin or similar material. The windings 27 may be energized separately or both at the same time, as required, by means of power circuit connections to be described hereafter.

Centrally located on the bottom inner surface of the shell 25 is a tube clamp 28 constructed with a plurality of spring fingers 29 adapted to receive and retain a thermostat tube 31. The tube clamp 28 is secured to the shell 25 by means of solder 32 to provide the thermal contact therebetween,

The cylinder 25 has lugs 33 which support a perforated insulating board end-closure 34 upon which are mounted terminals for various power connections to be described hereafter. In assembled position the thermostat tube 31, projects through the perforation. of end-closure 34 and the thermostat leads are connected in the power circuit. Also extending through the perforation in the end-closure 34 is an L-shaped metallic member 35'preferably of copper. The member 35 has a relatively long arm 36 extending in direct contact with the lower surface of the tube 31 and insulated from the inner surface of the tube clamp 28 by means of a strip 37 of suitable insulating material, such as glass fiber. The short extension of the L-shaped member 35 'is formed in theshape of a spade lug with a slot 38 therein.

Two power terminals 41 on the end-closure 34 are provided to receive a pair of spring metal strips 42 secured therein with a high melting point solder. The spring metal strips 42 may be of Phosphor bronze or other suitable material and are soldered with the high melting point solder to .the terminals 41 in a position to be normally not in contact with each other. In the assembly of the temperature control unit the spring strips 42 are depressed into a position of approximate-contact and a bridging solder connection 42 therebetween is made with a predetermined low melting point solder.

The power connections from the terminals on the endclosure 34 are made by means. of wire leads 45 which connect to appropriate power pins of the socket 12.- The leads 45 are of sufiicient length to permit the shell 25 to beslidably removed from the mounting plate 13. for the purpose. of inserting and removing appropriate crystal units in their operative position plugged into the sockets 17.- Also connected to pins of the socket 12 are a. resistor 47 and capacitor 48 which are circuit connected to protect the contacts of the thermostat tube 31 as will be described hereinafter.

Referring now to Fig. 2, the assembled relation of the elements of the crystal ovencan be seen as obtained by mounting the cylindrical member 25 on the plate 13 with two crystal units 46 therein. Over the assembled oven a blanket of fiber glass insulation 51 of substantial thickness is placed and the outer shell 52 of copper or other suitable metal is placed to enclose the entire assembly. The outer case 52 fits the periphery of the base 11 and is secured thereto by means of screws 53 which are in sliding engagement with the case 52 by means of slots in the edge thereof; One of the screws 53 also engages the slot 38 in the thermal anticipator unit 35, the short end of which is in continuous thermal contact with the inner surface of the case 52 along its entire length.

In Fig. 3 the power connections on the terminals of the end-closure plate 34 are shown. These connections provide terminals for the power leads 45 and their connection with the leads of the thermostat tube 31, the thermal cutout terminals 42 and the heater windings 54.

The electrical connections for the signal and the power circuits of the crystal oven are shown in Fig. 4. For the power circuits, terminals 1, 3, and 7 of the plug 12 are connected as shown, terminals 1 and 3 being connected to one end of respective heater windings 27. The other ends of the heater windings 27 are joined and connected to one of the terminals 41 of the thermal overload device 42. Terminal 5 is a power terminal and a test point connected to the joined terminals of the heater windings 27. The other of the terminals 41 is connected to one of the leads of the thermostat tube 31, the other lead of which is connected to pin '7 of the socket 12. Con nected across the thermostat and thermal cut-out elements is the resistor-capacitor circuit 47, 48.

Signal circuits are completed by connecting the individual crystal socket leads to the four terminals 24 from which the resistors 22 and capacitors 23 are connected respectively to the four terminals '21; The terminals '4; 21 are respectively connected to leads 2, 4, 6 and 8 of the plug 12 as shown in Fig. 4.

In the operation of the crystal oven of this invention the unit is plugged into operating equipment in the assembled form as shown in Fig. 2. Prior to final use the unit is assembled at the place of manufacture and suitably adjusted and calibrated by the proper selection and connection of the capacitors .23-and resistors 22 on the terminal board 19. Once having these circuit constants selectedthe assembled crystal unit can be pluggedinto the operating equipment without further adjustment thereof or change in the crystal assembly. In a'similar manner when a crystal unit is required to be replaced or removed for any reason, the assembly can be taken apart and the crystal elements 46-removed without any disruption or change in the lead dress of the signal leads associated with the terminal board 19.

In operating-condition the oven provides intimate thermal contact between the thermostat tube 31 and the oven housing-25 by means of the tube clamp 28. Anticipation of'the correction required by changing temperatureis provided by means of the L-shapcdmember 34 being in thermal contact with the tube 31 and the interior surface of the case 52 while the longer portion of the L-shaped.member 36..is.insulated from the base of the tube clamp;28. In theevent of malfunctioning. of the thermostat such that thercontactsthereof remain closed the heater would remain energizedandthe temperature. within. the ovencouldrise to a level which would be dangerouszand cause permanent damage to :thecrystal.

units. 46; To. avoidthis .difliculty the thermal cut-out contacts-42..are.-maintained. in. connected relation by, means: of the low melting point. solder.43 which is selected to have a melting point at a temperature slightlyv above the maximum operating'temperature of the oven. Inthe event the interior temperature approaches a. point which 'is dangerous to the crystal units, the low-melting point solder 43 will release the spring contacts-42 and permanentlydeenergize the heater windings 27.

It is apparent from the foregoing description that the present invention provides'a simple, compactand reliable crystaloven for maintaining a plurality of crystals at exactly .thesame temperature while accurately maintaining that temperature irrespective of the ambient conditions. It also provides means for protecting the crystal units from excessive temperatures due to malfunctioning of the thermostat. Theentire unit can be assembled and disassembled at will without disturbing the critical circuits'and' the signal circuits: may be adjusted to im-- pedance and related electrical quantities at will to con-- form. to the requirements of a particular application.

While many modifications of the present invention will be apparent inth'e lightof the above teachings, such modificationsxwithin:the.scope of the :appendedclaim are .understood to be -withinthe scope 'of the invention;

I claim:

A temperature regulated frequencycontrol uniteom prising 'a supporting base, a plug mounted'on said base withlindividual power and signal pin connectors projecting fromone side of said'base and passing therethrough for circuit connections on the other side of said base, a support plate fixed to said base on said other side and displaced with respect to said-plug, a pair of crystal sockets secured to said plate in spaced parallel relation for supporting two'plug-in crystal units equidistant from and substantially symmetrically above said base, a metal cylinder removably secured and fitted to the periphery of said plate and enclosing the space occupied by said crystal units when inserted in said sockets, a heater winding on the outer surface of said cylinder, a tube clamp fixed to the inside surface of said cylinder to lie parallel to and between said crystal units in assembled position, a perforated insulating board end-closure for said cylinder having power terminals thereon, a thin metal strip bent in L-shape-witlr the longer portion extending through one of said perforations and lying flat along the inner surface of said tube clamp and the shorter portion extending along the edge of said base, a thin strip of thermal insulation between said strip and said inner surface, a glass thermostat tube having thermostatic control contacts and releasably secured by said tube clamp in thermal contact with said strip, a thermal cut-out means comprising a pair of resilient metal strips mounted in non-contacting normal position to two of said power terminals respectively and retained in biased contacting position solely by a connection of predetermined melting point solder, means for making said control unit testable when said metal cylinder is removed from the periphery of said plate comprising lead wire connections of suflicient length from said power pin connectors to terminals of said heater windings for maintaining circuit connections through said thermostatic control contacts and said thermal cut-out when said cylinder is in said removed condition, a terminal board mounted parallel to said support plate on the side opposite said crystal sockets, a first set of terminals on said terminal board respectively connected to the crystal terminals of said sockets, a second set of terminals on said terminal board connected respectively to said signal pin connectors, a resistor and capacitor mounted on said terminal board and removably connected between said sets of terminals in series with each of said crystals in said sockets, and a metal case removably fitted to said base and enclosing the assembly formed by said cylinder, said plate, said end-closure and said terminal board, a relatively thick lining of thermal insulation inside said case, said lining lying between said case and said cylinder, fastening means removably securing said case to said base and means for maintaining said shorter portion of said strip in intimate thermal contact with the inner surface of said case throughout the entire length of said shorter portion.

References Cited in the file of this patent UNITED STATES PATENTS 395,421 Cockburn Jan. 1, 1889 1,264,868 Carlson Apr. 30, 1918 1,595,598 Brennan Aug. 10, 1926 2,102,783 Bokovoy Dec. 21, 1937 2,470,134 Bitner May 17, 1949 2,493,145 Iaiiee Jan. 3, 1950 2,727,110 Von Hoorn Dec. 13, 1955 

